The present invention relates to a variable speed rotary drive mechanism. More specifically, the present invention includes a drive mechanism useful in operating display sign elements, such as those on prismatic displays, so as to vary the speed of rotation from a maximum velocity occurring during the changing of display surfaces to a minimum velocity occurring as the position corresponding to the display of the desired surface is approached.
There are several known kinds of convertible signs, one type of which creates a display arrangement comprising single or multiple prisms, each of which are mounted at opposite longitudinal ends and rotatable about their longitudinal axis. in the case of multiple prisms, each prism is part of an equal sequence in a frame, the prisms residing beside each other. The sides of the prism are oriented in a permanently occurring sequence forming a number of displays corresponding to the number of side surfaces of the single prism. Such a sign necessarily includes a drive motor for synchronous rotation of the prisms via a transmission.
Displays of this type usually comprise triangular aluminum prisms, which rotate in an aluminum frame and show three displays in permanently recurring sequence. The prisms can be dismounted and exchanged. Due to the triangular shape of the prisms, three different views can be shown. The display arrangement can be mounted with its frame standing free, on walls or on roofs of buildings. Also, single prism signs are typically found on scoreboards in arenas or the like.
Known display arrangements of this type are typically driven by an electric motor, and the prisms are rotated synchronously by a gear transmission in such a manner that the sides of the respective prisms belonging to the same picture are shown simultaneously and form a display. The gear transmission ensures synchronous rotation of each prism.
A gear transmission, however, involves certain disadvantages. A desirable characteristic of most convertible signs is that they operate noiselessly, particularly when the displays are mounted on buildings. A gear transmission for operating noiselessly requires good lubrication. This requirement would be difficult to attend to at many sign locations, because of the need for periodic service and such signs in most cases are positioned in places of difficult access. The problem of access has created a need for mechanisms of high durability and reliability, along with the continuing requirement for accurate registration of the sign elements and the constant need to start, rotate and stop the sign display. Experience in the field has demonstrated the need to convert this inherently complex mechanical operation into one having as much reliability and simplicity as possible.
A recent solution to these problems is disclosed in commonly assigned U.S. Pat. No. 5,343,645, issued to Huber. There is disclosed a chain driven gear drive system, including off-center gear elements. These gear elements are rotated to translate various potential speeds to a mounting gear, on which a sign member is mounted. As a result of this structure, the sign member rotates through successive 120xc2x0 turns while varying the speed of rotation from a maximum velocity occurring during the changing of display surfaces to a minimum velocity occurring as the position corresponding to the new display surface of the sign member, of the sign is approached.
What is needed is an alternate drive mechanism for driving display sign arrangements and other devices that require frequent start and stops.
The present invention provides an alternate variable speed rotary drive mechanism for operating display sign elements, such as those on prismatic displays, so as to vary the speed of rotation from a maximum velocity occurring during the changing of display surfaces to a minimum velocity occurring as the position corresponding to the display of the desired surface is approached. The variable speed rotary drive mechanism can also be used to drive other devices requiring frequent starts and stops, such as conveyors.
In one embodiment in accordance with the invention, a convertible sign mechanism is provided which comprises a convertible sign member that is rotatable about an axis. A drive means is connected to the convertible sign member for rotating the convertible sign member at a variable velocity, with the drive means operating continuously throughout the rotation of the convertible sign member. The drive means includes a motor, a drive shaft operatively connected to the motor, a cam follower operatively connected to the drive shaft, a member configured to receive the cam follower in a slidable engagement, an output gear operatively connected to the member; and a drive gear operatively connected to the output gear and to the convertible sign member. The output gear and the drive gear provide a reduction ratio of at least 2:1.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages and objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying description, in which there is described a preferred embodiment of the invention.